Renal tubular vasopressin receptors downregulated by dehydration

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Abstract
Receptors for arginine vasopressin (AVP) were characterized in tubular epithelial basolateral membranes (BL membranes) prepared from the kidneys of male Sprague-Dawley rats. Association of [3H]AVP was rapid, reversible, and specific. Saturation studies revealed a single class of saturable binding sites with a maximal binding (Bmax) of 184 +/- 15 fmol/mg protein and a KD of 0.61 +/- 0.04 nM. IC50S for AVP, lysine vasopressin, and oxytocin were 0.74 nM, 9.7 nM, and greater than 1 microM, respectively. The V2 receptor antagonist was more than 3,700 times as effective in displacing [3H]AVP than was the V1 antagonist. To investigate the physiological regulation of vasopressin receptors, the effects of elevated levels of circulating AVP on receptor characteristics were studied. Seventy-two-hour water deprivation significantly elevated plasma osmolality and caused an 11.5-fold increase in plasma [AVP]. Scatchard analysis revealed a 38% decrease in the number of AVP receptors on the BL membranes from dehydrated animals. The high-affinity binding sites on the BL membranes fit the pharmacological profile for adenylate cyclase-linked vasopressin receptors (V2), which mediate the antidiuretic action of the hormone. We conclude that physiologically elevated levels of AVP can downregulate vasopressin receptors in the kidney.